Ziyad bin Hudayr said: Sayyiduna Umar (may Allah be pleased with him) sent me to the Christians of Banu Taghlib and ordered me to collect a twentieth of their wealth, and he forbade me to collect the tithe from any Muslim, or from a dhimmi who pays the kharaj (land tax). He said: By "Muslim" is meant one of them who becomes Muslim, because he had sent him to the Christians of Banu Taghlib; and from a dhimmi the tithe is not collected on livestock, crops and fruits, except from Banu Taghlib, because peace was made with them on exactly that basis. The Shaykh said: It is also possible that the peace terms of the dhimmis who were under his authority did not include collecting a tithe on their trade goods.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجزية / 18805